A teenager frantically pleaded with her cousin to slow down moments before a Fast and Furious style drunken car race ended in a horrific crash which killed both her and her sister.

Brooklyn Morehu-Clark, 13, was killed when the car she was thrown from landed on top of her, while her sister, Merepeka Morehu-Clark, 14, was thrown behind the car and died instantly. Neither was wearing a seatbelt.

Yesterday her cousin, Hetaraka Hikurangi Reihana, 21, went on trial for their manslaughter in the High Court in Hamilton.

He was the driver of the car that crashed on Welcome Bay Rd, Tauranga, on Christmas Day, 2011. Joining him in the dock was the girls' mother, Phillippa Vanessa Morehu, 37, and another of their cousins Haki Tetuere Davey, 18, who are jointly charged with manslaughter.

Crown prosecutor Greg Hollister-Jones said that while Reihana was the one driving the car that crashed, all three were to blame because they were racing - at speeds of up to 140kmh - before the crash happened.

"Each of these individuals clearly influenced the driving of the other two - that's critical," he told the jury.

"This was deliberate - it was a set-up, premeditated and sustained course of racing by three people who knew each other to be drunk."

The court was told all three had been drinking heavily before they got in the cars and headed to a nearby family burial ground. Reihana had between six and eight cans of pre-mixed bourbon, and about six shots of vodka.

Joining him in the front of the car were another of Morehu's daughters holding his daughter, while the sisters sat in the back.

Later tests showed Reihana had 157 micrograms of alcohol in his blood - almost two times the legal limit.

Davey had drunk both shots of vodka and several cans of 8 per cent bourbon before driving, while Morehu had about nine bottles of beer.

However, they were never formally breath tested. Davey was a forbidden driver, while Morehu was a restricted driver.

Mr Hollister-Jones said had Morehu and Davey not acted to keep the race going, Reihana would have had no-one to race.

But lawyers for both Morehu and Davey, Paul Mabey QC and Glenn Dixon respectively, said the Crown needed to prove that their clients were party to the racing, to be found guilty.

In his opening address, Mr Hollister-Jones said one witness described the driving he saw as like that from the Fast and Furious - a movie franchise which depicts high speed street racing.

The three cars were seen travelling closely, at speed, along Welcome Bay Rd before the crash. During the race, one of the sisters told Reihana she was scared and asked him to slow down.

As Reihana overtook the two cars ahead of a blind corner he lost control, fishtailing before sliding down the wrong side and straight into the path of an oncoming ute. The force caused the ute to flip backwards, landing on its roof.

Its driver, Brett McCready, yesterday told the court he had nowhere to go. "So just before impact I slammed on the brakes ... The next thing I'm sort of upside down."